Hydraulic vs mechanical gearbox.

[a64pilot]

My preference would be for straight mechanical, with a multi plate wet clutch, one driven by helical gears so that the higher the torque placed on them, the tighter they are compressed. This solves the hard engagement issue, and will keep the clutch pack from ever slipping under load.
A multi plate wet clutch pack is what is used to harness motorcycle engines that make in the hundreds of HP, and of course you’re left hand disengages the clutch every shift so there is no tough engagement either.
However motorcycles don’t usually have helical cut gears that force the plates together, they usually rely purely on Springs.
Cone clutches have been and are a source of problems. I assume they must be cheaper to manufacture, cause I can’t come up with any reason to use them myself.

[GILow]

Originally Posted by Uncle Bob

When I acquired my boat it had a hurth box attached to one of John's 50 hp engines and it started to slip at around 860 hrs, his advice was that he no longer supplied those boxes and recommended a PRM mechanical replacement, almost a direct drop in for not much more than the cost of having the Hurth rebuilt. So far so good.

Hmmmm.... he had lots of gearbox options, including options he didn’t recommend. Which was weird. I suspect one of the non recommendations might have been the Hurth. Overall, I came away from my call to him feeling more worried than when I started.

[GILow]

Originally Posted by Uncle Bob

When I acquired my boat it had a hurth box attached to one of John's 50 hp engines and it started to slip at around 860 hrs, his advice was that he no longer supplied those boxes and recommended a PRM mechanical replacement, almost a direct drop in for not much more than the cost of having the Hurth rebuilt. So far so good.

Seems Beta only offer a hydraulic PRM as standard, their standard mechanical boxes are either ZF or TMC.

[FPNC]

For a 50 hp engine turning a Kiwi, the mechanical gear box is a good choice. If your replacing a Borg Warner inline gear, reuse the old transmission if practical.

[GILow]

Originally Posted by a64pilot

My preference would be for straight mechanical, with a multi plate wet clutch, one driven by helical gears so that the higher the torque placed on them, the tighter they are compressed. This solves the hard engagement issue, and will keep the clutch pack from ever slipping under load.
A multi plate wet clutch pack is what is used to harness motorcycle engines that make in the hundreds of HP, and of course you’re left hand disengages the clutch every shift so there is no tough engagement either.
However motorcycles don’t usually have helical cut gears that force the plates together, they usually rely purely on Springs.
Cone clutches have been and are a source of problems. I assume they must be cheaper to manufacture, cause I can’t come up with any reason to use them myself.

I think the ZF offering with the Beta meets your recommendations?


https://www.performancediesel.com/wp...oads/ZF25M.pdf

[transmitterdan]

Originally Posted by GILow

I think the ZF offering with the Beta meets your recommendations?


https://www.performancediesel.com/wp...oads/ZF25M.pdf

Unless you plan to motor a lot the ZF-15 is adequate for a 42 when powered by the Beta or other 50HP engine. It does not have an oil cooler but it’s a good idea to get the bolt on water cooler. It cools the case but there is no oil leaving the gear box.

[Siberian Sea]

I installed a Beta Marine with a Twin Disc hydraulic gearbox. Had these for years in my commercial fishing boats in Alaska. Fishing operations would work the hell out of the gearbox and never never did I have a problem. Honestly an Alison or Twin Disc gearbox is second to none. These are good for the life of the boat. Yes they are big and heavy but, just like your anchor gear it’s something you never want to fail.

[DougR]

First off I would suggest that which ever gear you select, you study the rating sheet for the gear in question.....Most gears have different torque (horsepower) ratings depending on the application. That is, they can accept more power when used in limited hour, recreational use than in light commercial applications, and even less in continuous commercial use. If your engine torque/rpm places you near the upper power limit for a given gearbox application, it's probably best to move to the next larger gearbox where the safety margin is greater.

That said its time to look at the differences between mechanical gears and hydraulic. Let's break things down into different topics, such as comfort, efficiency, etc...

-efficiency- This is a rating which describes the amount of power available at the output shaft compared to the power on the input shaft. There is power lost in all gearboxes, and these losses come from gear and bearing friction, oil churning losses and pumping losses. Both types have friction and oil churning losses, but hydraulic gearboxes also have oil pumps to develop the pressure necessary to squeeze the clutch packs together, and these oil pumps absorb power, so mechanical gearboxes are almost always more efficient than hydraulic. How much more efficient? Could be the difference between 2% loss or 4% loss, or even more. 2% of 50 h.p. is 1 hp. Is that significant to you? Would you like to spend 2% more on fuel over the life of the engine?....
Where does this loss power go? It goes into heat, and for that reason most hydraulic gears have gear coolers and they are usually remote from the gear and connected with hoses. This cooler could be a maintenance item and that needs to be considered. Some mechanical gears also have coolers, but they are usually integral to the gear case and don't present as much of a maintenance issue.

-Comfort and ease of operation- You might say " how can a gear box effect comfort?" Well, mechanical gears usually require you to move a shift cone, or a sliding sleeve, or something like that when you shift gears, but hydraulic gears shift by rotating a valve body. It's not at all uncommon to find that when shifting, the effort required to move the sliding sleeve or cone clutch becomes a two handed affair, particularly when trying to come out of gear. Hydraulic gear shifting, on the other hand, is basically a fingertip exercise. Not only that, but mechanical gear shifting is often accompanied by a resounding "clunk" when the gear engages. Which Is more important to you?

-Prop compatability- When sailing with the engine turned off, hydraulic gears are always in neutral and that normally means that there is nothing that will prevent the shaft from rotating. Do you care if the prop rotates under sail? Will your prop feather or fold if the shaft is able to rotate?
Some mechanical gears can be placed in reverse position to stop shaft rotation when sailing. Other mechanical gear manufacturers do not allow the gearbox to be in gear when sailing. You might want to check into this for your particular brand of gearbox and prop type.

Hope this point out a few items and maybe raises a few questions for you.

DougR

[roland stockham]

Only thing nobody has yet mentioned is that hydraulic gearboxes may be heavier duty and have an oil cooler. In commercial applications that can be an advantage or where you anticipate long runs under motor or heavy loads.

[stormalong]

Originally Posted by Jim Cate

Our 43 hp Nanni/Kubota has a Hurth/ZF 10 mechanical box. The original one failed just after we bought the boat, and I replaced it with like... nervously. Those trannies don't have a good reputation, but ours now has >5000 hours and is still working as new. Go figger! But I've changed the ATF religiously with every oil change (<200 hours) and that is apparently quite important with these gears. They only hold 350 mL, and it gets damn hot at times, so short life time.

I believe that Beta offers a better mechanical box on the 50 (which is a slightly larger displacement version of ours) and I'd have no worries about that one. If they offer a bigger one as optional, I'd go for that, just in case~

Jim

Jim, Do you have a cooler on your Hurth/ZF? I have a ZF M15V (Hurth 150V) transmission on my Beta 50 and it has a cooler. ZF coolers are bolted to the side of the tranny and have raw water circulating through them.

These transmissions have had a bad reputation for short life. My experience has been different. I am on my second one in 29 years owning the same boat. The first one started dripping oil from the quill shaft seal and speedy sleeves and new seals would not stop the drip. The cost of servicing these is so high that I chose to replace it. It was 25 years old and had around 9,000 hours when replaced. I think the failure may have been not changing the oil (ATF) often enough and on the new one I change it more often.

[Cadence]

I'm pro a crash box. Any fool can rebuild one. Hydraulics are great just not hidden inside a casing.

[Jim Cate]

Originally Posted by stormalong

Jim, Do you have a cooler on your Hurth/ZF? I have a ZF M15V (Hurth 150V) transmission on my Beta 50 and it has a cooler. ZF coolers are bolted to the side of the tranny and have raw water circulating through them.

These transmissions have had a bad reputation for short life. My experience has been different. I am on my second one in 29 years owning the same boat. The first one started dripping oil from the quill shaft seal and speedy sleeves and new seals would not stop the drip. The cost of servicing these is so high that I chose to replace it. It was 25 years old and had around 9,000 hours when replaced. I think the failure may have been not changing the oil (ATF) often enough and on the new one I change it more often.

Nope, no cooler, though I have often thought about adding one.

After the original Hurth 100 failed, I did some internet research and the upshot was that very frequent ATF changes were recommended by lots of "experts". Their consensus was enough to convince me, and so far the practice has been successful... ie changing ATF with each oil change for the engine.

Jim

[patprice]

Originally Posted by Uncle Bob

Hi I have to agree with Ann, however I would take a look at WM Diesel, Kubota based and very well put together by John Wichard in Sydney.
Regarding the gearbox, the only offering I can add is avoid multi plate systems like the hurth!

YES
I installed a WM Diesel in my Swanson 36 in 2006. The engine has been brilliant.
But the Hurth gearbox(s), yes plural, were a disaster. Now have a PRM box, all good.

[jamhass]

In some cases, a hydraulic tranny will not stop a feathering prop without a shaft brake and the shaft continues to turn when sailing with the engine off.

[chrisr]

I have always had mechanical gearboxes, however did charter a canal boat in europe a while ago, with a hydraulic g'box...and it was an eye-opener for boat handling

the ability to go from full ahead to full astern as fast as you could move the lever was impressive, and allowed one to turn a 55'single screw in not much more than it's own length

of course there are other issues, however hydraulic has (apparently) a big advantage in boat handling.

cheers,